Acid alpha-mannosidase (also known as lysosomal alpha-mannosidase or MAN2B1) is a crucial lysosomal hydrolase enzyme encoded by the MAN2B1 gene. This enzyme catalyzes the hydrolysis of terminal alpha-mannose residues from mannose-containing oligosaccharides, playing an essential role in glycoprotein catabolism within lysosomes. Deficiency of this enzyme causes alpha-mannosidosis, a rare lysosomal storage disorder.
| Attribute |
Value |
| Protein Name |
Acid Alpha-Mannosidase |
| Gene |
MAN2B1 |
| UniProt ID |
O00754 |
| Molecular Weight |
~280 kDa (homodimer) |
| Length |
1,001 amino acids (precursor) |
| Subcellular Localization |
Lysosome |
| Protein Family |
Glycoside hydrolase family 38 |
Acid alpha-mannosidase is a lysosomal hydrolase with the following structural features:
- Precursor Form: 1,001 amino acid precursor
- Proteolytic Processing: Cleaved into heavy chain (~70 kDa) and light chain (~30 kDa)
- N-glycosylation: Multiple N-linked glycosylation sites essential for proper folding and lysosomal targeting
- Mannose-6-phosphate Tags: Required for lysosomal trafficking via mannose-6-phosphate receptors
- Active Site: Contains catalytic residues for mannose hydrolysis
The enzyme requires optimal acidic pH (around 4.5-5.0) for activity, consistent with the lysosomal environment.
Acid alpha-mannosidase plays a critical role in glycoprotein catabolism:
- Oligosaccharide Degradation: Hydrolyzes terminal alpha-1,2-, alpha-1,3-, and alpha-1,6-linked mannose residues from N-linked glycans
- Glycoprotein Turnover: Essential for normal degradation of glycoproteins in the lysosome
- Cellular Homeostasis: Prevents accumulation of mannose-rich oligosaccharides
The enzyme works in concert with other lysosomal hydrolases to completely degrade complex N-linked glycoproteins.
Deficiency of acid alpha-mannosidase leads to accumulation of mannose-rich oligosaccharides in lysosomes throughout the body, particularly affecting:
- Central Nervous System: Accumulation in neurons leads to intellectual disability, ataxia, and developmental delays
- Cochlea: Accumulation causes hearing loss
- Bone: Storage leads to dysostosis multiplex and skeletal abnormalities
- Immune System: Abnormal glycoprotein degradation causes immunodeficiency
Disease Severity: Correlates with residual enzyme activity - patients with <1% activity have severe phenotype, while 1-10% activity shows milder disease.
- Enzyme Replacement Therapy (ERT): Recombinant human alpha-mannosidase (Velmanase alfa) approved for treating alpha-mannosidosis
- Bone Marrow Transplant: Can provide donor-derived enzyme-producing cells
- Gene Therapy: Experimental approaches using viral vectors to deliver functional MAN2B1
- Substrate Reduction Therapy: Experimental approaches to reduce substrate accumulation
- Chaperone Therapy: Small molecule chaperones to enhance residual enzyme activity
- Desnick et al., Enzyme replacement therapy for alpha-mannosidosis (2004)
- Borgwardt et al., Clinical efficacy of velmanase alfa (2015)
- Malm & Nilssen, Alpha-mannosidosis (2008)
- Desnick et al., Enzyme replacement therapy for alpha-mannosidosis (2004)
- Borgwardt et al., Clinical efficacy of velmanase alfa (2015)
- Malm & Nilssen, Alpha-mannosidosis (2008)